Here is my patch proposal: it makes usage of an HTTP HEAD call which is used in few other place so it's safe to adopt it here too. The debug message cannot be simplified into a set of predefined error messages, to help the troubleshooting.

Now, I'll look at the issue in the forum (where everything started): it could be this issue not related with the original post but with Dan's reply.

Fixed a small typo (use => used) in a comment inside scorm_check_url().

Damn' flu! Just realized that:

1. the branch name was incorrect
2. more important the coding style for the nested if was tremendous :

   +            } else {
   +                // Availability check.
   +                if ($errormsg = scorm_check_url($reference)) {
   +                    $errors['packageurl'] = $errormsg;
   +                }
                }
   

thanks Matteo - took a quick look and it looks ok - couple of extra carriage returns in the patch that might not be needed but I haven't actually looked at the full code so it might make sense to have those in the patch? - I'll try to do a proper peer review on this later this week - if I haven't done it by Thurs ping me again to take a look!

Ping!
L2R419 and L2R429 are there according to the style used for the previous check "blocks" i.e added intentionally.

looking again..

not sure what I think about returning false on success? - my personal preference for functions would be to return true when no error is found - although I'm not sure what the integrators think about that.

yeah - just had a chat with Sam H - returning true or error string would be more consistent with the rest of Moodle rather than false or error string - would you mind changing that? - thanks!

OK
false|string was selected to let the code consuming be compact enough: BTW, I'll do the required changes.

Hi Dan,
here is the code using true|string, rebased against 2.4beta+ (Build: 20121123).

cool - looks ok to me - bouncing up for integration. not completely sure about the is_string() stuff but will leave the integrator to make a call on that. Thanks Matteo!

Integrated (24 and master).

I don't think we should be backporting this to older stables, as far as may be considered an improvement.

Thanks!

works as described.
passing
Thanks

Many thanks for your effort, the whole Moodle Community will be enjoying your great solutions starting now!

Closing, ciao